Interface for UV-curable adhesives

ABSTRACT

In an embodiment of this invention, an adhesion layer is deposited on an encapsulation lid to provide strong adhesion with the UV-curable adhesive in order to improve encapsulation of an organic electronic device. The adhesion layer is comprised of a metallic layer or a ceramic layer that is thin enough to be nonopaque and thick enough to provide stronger adhesion at an interface with said UV-curable adhesive than said encapsulation lid.

BACKGROUND OF THE INVENTION

An organic electronic device such as an organic light emitting diode(“OLED”) (the OLED can be used in, for example, a display or as a lightsource element of a light source), an organic light sensor, an organictransistor, an organic solar cell, or an organic laser requireprotection from oxygen and moisture in the atmosphere, and thereforeemploy some form of encapsulation. One common procedure to encapsulatethe organic electronic device is to sandwich it between a substrate andan encapsulation lid, and an adhesive around the perimeter of the deviceholds together the substrate and the encapsulation lid such that thereis a continuous perimeter seal around the device.

OLEDs, in general, are known in the art and are discussed in, forexample, U.S. Pat. No. 5,457,565 entitled “Organic ElectroluminescentDevice”. Organic light sensors, in general, are also known in the artand are discussed in, for example, U.S. Pat. No. 6,483,099 entitled“Organic Diodes with Switchable Photosensitivity”. Organic transistors,in general, are known in the art and are discussed in, for example, U.S.Pat. No. 6,485,884 entitled “Method for Patterning Oriented Materialsfor Organic Electronic Displays and Devices.” Organic solar cells arealso known in the art and are discussed in, for example, U.S. Pat. No.4,963,196 entitled “Organic Solar Cell”. Organic lasers are known in theart and are discussed in, for example, U.S. Pat. No. 5,881,089 entitled“Article Comprising an Organic Laser”.

When manufacturing an organic electronic device, adhesives that providelow total accumulated cycle (“TAC”) times and that remain stable or areworkable over extended periods of time are desirable. Thermal-cureadhesives can be used to manufacture the organic electronic device butthey have long TAC times (e.g., thermal-cure adhesives typically take anhour to cure) and is workable for only a short time (e.g., once theresin is mixed, the thermal-cure adhesive will typically cure after anhour or even less and the curing can occur anywhere, even in thedispensing equipment). On the other hand, UV-curable adhesives can curevery quickly when exposed to UV radiation (e.g., UV-curable adhesiveshave a low TAC time typically about ninety seconds), yet remain stableor workable for long periods until triggered by the UV radiation at auser-designated point in the process sequence. These characteristics,among others, make it desirable to use UV-curable adhesives to form theperimeter seal to encapsulate the organic electronic device.

In terms of degradation caused by the environment, the electronicdevice's lifetime is related to the permeation rate of oxygen andparticularly water across this perimeter seal (the permeation ratethrough the substrates is generally negligible). This permeation rate isa sum of the permeation through the bulk of the sealing material (“bulkdiffusion”) and permeation along the interfaces between the sealingmaterial and the substrate or encapsulation lid (“interface diffusion”).When the bonding to the encapsulation lid is weak (i.e., there's pooradhesion), permeation along this interface can be high, greatlyshortening the device lifetime. Furthermore, poor adhesion can lead todelamination during mechanical processes such as scribe and break (i.e.,device singulation). Therefore, strong adhesion to the encapsulation lidis important to effectively encapsulate the elements.

FIG. 1 shows a prior art encapsulated organic electronic device 106. InFIG. 1, an organic electronic device 115 is fabricated on a substrate118. As stated earlier, the organic electronic device 115 can be anOLED, an organic light sensor, an organic transistor, an organic solarcell, or an organic laser. A UV-curable adhesive 112 is applied aroundthe perimeter of the organic electronic device 115. An encapsulation lid109 is placed on the UV-curable adhesive 112 in order to encapsulate theorganic electronic device 115. The encapsulation lid 109 is nonopaque.The substrate 118 and the encapsulation lid 109 are moved together sothat the UV-curable adhesive 112 is in contact with both the substrate118 and the encapsulation lid 109. Then, UV radiation is applied to theUV-curable adhesive 112 in order to cure it (e.g., the adhesive absorbsthe UV-radiation and transfers that energy to cross-link the adhesivegroups so that the adhesive becomes rigid). One of the disadvantages ofthis configuration is that over time, delamination typically occurs atthe interface between the UV-curable adhesive 112 and the encapsulationlid 109.

In order to decrease the likelihood of delamination and improveadhesion, an additional adhesion layer is typically incorporated.Incorporating the adhesion layer to improve encapsulation of the organicelectronic device is not effective if UV-curable adhesive is also usedsince the materials that are good adhesion layers typically require athickness that makes them opaque. FIG. 2 shows the prior art use of theadhesion layer extended to organic electronic device encapsulation. InFIG. 2, an organic electronic device 115 is fabricated on a substrate118. An opaque adhesion layer 221 is deposited on the encapsulation lid209. A UV-curable adhesive 112 is applied on the substrate 118 aroundthe perimeter of the organic electronic device 115, or alternatively,applied on the opaque adhesion layer 221 such that when theencapsulation lid 209, the substrate 118, and the UV-curable adhesive112 are brought together, the organic electronic device 115 is sealedaround its perimeter. After the UV-curable adhesive is applied, thesubstrate 118 and the encapsulation lid 209 are moved together so thatthe UV-curable adhesive 112 is in contact with both the substrate 118and the opaque adhesion layer 221 to seal the organic electronic device.Because this adhesion layer is opaque, UV radiation will not reach theUV-curable adhesive 112 to cure that adhesive. Therefore, one of thedisadvantages of this configuration is that UV-curable adhesive cannotbe used. A thermal-cure adhesive can be used, but this adhesive resultsin high TAC times and is workable for only a short time.

For the foregoing reasons, there exists a need to encapsulate theorganic electronic device using a UV-curable adhesive such that there isstrong adhesion at the interface between the UV-curable adhesive and theencapsulation lid.

SUMMARY

An embodiment of an encapsulated organic electronic device is describedthat has strong adhesion between the components that encapsulate thedevice. The embodiment of the encapsulated device includes a substrate,an organic electronic device on the substrate, and a UV-curable adhesiveon the substrate where the UV-curable adhesive is applied such that itsurrounds a perimeter of the organic electronic device. The encapsulateddevice also includes an adhesion layer on the UV-curable adhesive, andan encapsulation lid that is on the adhesion layer. The encapsulationlid is nonopaque, and the adhesion layer is made of a metallic layer ora ceramic layer that is thin enough to be nonopaque and thick enough toprovide stronger adhesion at an interface with the UV-curable adhesivethan the encapsulation lid.

An embodiment of a method to encapsulate an organic electronic device isdescribed that provides strong adhesion between the components thatencapsulate the device. The embodiment of this method includesfabricating the organic electronic device on a substrate, and depositingan adhesion layer on an encapsulation lid. The adhesion layer is made ofa metallic layer or a ceramic layer that is thin enough to be nonopaqueand thick enough to provide stronger adhesion than the encapsulationlid. The method further includes applying a UV-curable adhesive on thesubstrate or on the adhesion layer such that when the encapsulation lid,the substrate, and the UV-curable adhesive are brought together, theorganic electronic device is sealed around its perimeter. The methodalso includes moving together the substrate and the encapsulation lidsuch that the UV-curable adhesive contacts the substrate and theadhesion layer to seal the organic electronic device around itsperimeter. The method further includes applying UV radiation to theUV-curable adhesive to cure it.

Another embodiment of an encapsulated organic electronic device isdescribed that has strong adhesion between the components thatencapsulate the device. This other embodiment of the encapsulated deviceincludes a substrate, an organic electronic device on the substrate, anda UV-curable adhesive that surrounds a perimeter of the organicelectronic device. The encapsulated device also includes an adhesionlayer on the UV-curable adhesive, and an encapsulation lid that is onthe adhesion layer. The adhesion layer is made of chromium or titaniumand is thin enough to be nonopaque and thick enough to provide strongeradhesion at an interface with the UV-curable adhesive than theencapsulation lid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art encapsulated organic electronic device.

FIG. 2 shows the prior art use of the adhesion layer extended to organicelectronic device encapsulation.

FIG. 3 shows an embodiment of an encapsulated organic electronic deviceaccording to the present invention.

FIG. 4 shows an embodiment of multiple organic electronic devices thatare encapsulated according to the present invention.

FIG. 5 shows an embodiment of a method to encapsulate an organicelectronic device according to the present invention.

DETAILED DESCRIPTION

In an embodiment of this invention, an adhesion layer is deposited on anencapsulation lid to provide strong adhesion with the UV-curableadhesive in order to improve encapsulation of an organic electronicdevice. The adhesion layer is comprised of a metallic layer or a ceramiclayer that is thin enough to be nonopaque and thick enough to providestronger adhesion at an interface with said UV-curable adhesive thansaid encapsulation lid. As used within the specification and the claims,the term “on” includes when layers are in physical contact and whenlayers are separated by one or more intervening layers.

FIG. 3 shows an embodiment of an encapsulated organic electronic device306 according to the present invention. In FIG. 3, an organic electronicdevice 115 is fabricated on a substrate 118. An adhesion layer 321 isdeposited on the encapsulation lid 309. The adhesion layer 321 iscomprised of a metallic layer or a ceramic layer that is thin enough tobe nonopaque to UV radiation and thick enough to provide strongeradhesion at the interface with the UV-curable adhesive 112 than theencapsulation lid 309. The adhesion layer 321 is comprised of,preferably, a metal or a metal alloy; more preferably, a transitionmetal or a transition metal alloy; most preferably, chromium, titanium,tantalum, tungsten, aluminum, nickel, vanadium, or an alloy thereof; andoptimally, chromium. Alternatively, the adhesion layer 321 is comprisedof ceramic and more specifically, an oxide, a carbide, a nitride, aboride, or a mixture thereof.

More specifically, with regards to the thickness of the adhesion layer321, it is preferably thin enough such that the transparency (e.g.,percentage of UV radiation passing through) of the adhesion layer 321provides a reasonable TAC time.

In the optimum configuration in which the adhesion layer 321 iscomprised of chromium, the optimum transparency of the chromium layer isapproximately fifty percent and the optimum thickness of the chromiumlayer is approximately fifty angstroms. This configuration can increasethe lifetime of the organic electronic device by a factor of two or moreand also eliminate premature failures of the organic electronic devicedue to poor encapsulation.

The encapsulation lid 309 is comprised of a nonopaque material.Preferably, the nonopaque material is glass, or alternatively plasticwith a barrier layer on the plastic. The barrier layer on the plasticprevents the moisture from contaminating the organic electronic device.This barrier layer is also nonopaque.

A UV-curable adhesive 112 is applied on the substrate 118 around theperimeter of the organic electronic device 115, or alternatively, theUV-curable adhesive 112 is applied on the adhesion layer 321 such thatwhen the encapsulation lid 309, the substrate 118, and the UV-curableadhesive 112 are brought together, the organic electronic device 115 issealed around its perimeter.

Because the adhesion layer 321 and the encapsulation lid 309 arenonopaque to UV radiation, UV radiation can pass through the layer andthe lid to the UV-curable adhesive 112 in order to cure that adhesive.Because the UV-curable adhesive 112 is used to encapsulate the organicelectronic device 115, the TAC time to cure the adhesive is reasonable.The reasonable TAC time to cure the adhesive is, for example, less thanfive minutes, preferably, about ninety seconds. Also, the UV-curableadhesive 112 remains stable or workable for long periods until somepoint in the process sequence where the user decides to apply UVradiation to cure the adhesive (i.e., the user designated point in theprocess sequence). Because the adhesion layer 321 provides betteradhesion than either of the encapsulation lids 109, 309, the adhesion isstronger at the interface between the UV-curable adhesive 112 and theadhesion layer 321 resulting in a decreased likelihood of delamination.

FIG. 4 shows an embodiment of multiple organic electronic devices thatare encapsulated according to the present invention. In this embodiment,the UV-curable adhesive 112 is applied on the substrate 118 around theperimeter of each of the organic electronic devices 415, 418, 421, oralternatively, the UV-curable adhesive is applied on the adhesion layer321 such that when the encapsulation lid 309, the substrate 118, and theUV-curable adhesive 112 are brought together, each of the organicelectronic devices 415, 418, 421 is sealed around its perimeter.Further, the UV-curable adhesive is applied such that there is a spacebetween the UV-curable adhesive encapsulating adjacent devices. Thespace allows each of the multiple organic electronic devices 415, 418,421 to be singulated at the edges of the UV-curable adhesive withoutsingulating at where the UV-curable adhesive resides; singulating atwhere the UV-curable adhesive resides can reduce the effectiveness ofthe encapsulation.

Because the adhesion layer 321 and the encapsulation lid 309 arenonopaque to UV radiation, UV radiation can pass through the layer andthe lid to the UV-curable adhesive 112 in order to cure that adhesive.

FIG. 5 shows an embodiment of a method to encapsulate an organicelectronic device according to the present invention. In block 503, anorganic electronic device is fabricated on a substrate. In block 506, anadhesion layer is deposited on an encapsulation lid. The adhesion layerincludes a metallic layer or a ceramic layer that is thin enough to benonopaque to UV radiation and thick enough to provide stronger adhesionat the interface with the UV-curable adhesive than the encapsulation lid309. The adhesion layer is comprised of, preferably, a metal or a metalalloy; more preferably, a transition metal or a transition metal alloy;most preferably, chromium, titanium, tantalum, tungsten, aluminum,nickel, vanadium, or an alloy thereof; and optimally, chromium.Alternatively, the adhesion layer is comprised of ceramic and morespecifically, an oxide, a carbide, a nitride, a boride, or a mixturethereof.

More specifically, with regards to the thickness of the adhesion layer,it is preferably thin enough such that the transparency (e.g.,percentage of UV radiation passing through) of the adhesion layerprovides a reasonable TAC time.

In block 509, a UV-curable adhesive is applied on the substrate alongthe perimeter of an organic electronic device, or alternatively, theUV-curable adhesive is applied on the adhesion layer such that when theencapsulation lid, the substrate, and the UV-curable adhesive arebrought together, the organic electronic device is sealed around itsperimeter.

In block 512, the substrate and the encapsulation lid are broughttogether such that the UV-curable adhesive contacts both the substrateand the adhesion layer so as to seal the organic electronic device. Inblock 515, UV radiation is applied to the UV-curable adhesive to cureit. Because the encapsulation lid and the adhesion layer are nonopaqueto UV radiation, the UV radiation passes through these two items toreach the UV-curable adhesive and cures it.

EXAMPLE

An OLED was fabricated on a substrate. A chromium layer was deposited bysputter coating onto an encapsulation lid made of glass. The chromiumlayer had a thickness of approximately fifty angstroms and passedthrough approximately fifty percent of the UV radiation. The UV-curableadhesive was applied on the substrate along the perimeter of the OLED.The substrate and the encapsulation lid were brought together such thatthe UV-curable adhesive contacted both the substrate and the adhesionlayer so as to seal the OLED. Use of the adhesion layer (i.e., thechromium layer), increased the lifetime of the OLED by a factor of twoor more and also eliminated premature failures of the OLED.

As any person of ordinary skill in the art of organic electronic devicefabrication will recognize from the description, figures, and examplesthat modifications and changes can be made to the embodiments of theinvention without departing from the scope of the invention defined bythe following claims.

1. An encapsulated organic electronic device, comprising: a substrate;an organic electronic device on said substrate; an ultraviolet(“UV”)-curable adhesive on said substrate, said UV-curable adhesivesurrounds a perimeter of said organic electronic device; an adhesionlayer on said UV-curable adhesive, wherein said adhesion layer iscomprised of tantalum or vanadium and is nonopaque to UV radiation; andan encapsulation lid directly on said adhesion layer, said encapsulationlid being nonopaque to UV radiation.
 2. The encapsulated organicelectronic device of claim 1 wherein said adhesion layer is comprised ofan alloy of tantalum or an alloy of vanadium.
 3. The encapsulatedorganic electronic device of claim 1 wherein said organic electronicdevice is an OLED, an organic transistor, an organic light sensor, anorganic solar cell, or an organic laser.
 4. A method to encapsulate anorganic electronic device, comprising fabricating said encapsulatedorganic electronic device of claim
 1. 5. The method of claim 4 whereinsaid adhesion layer is thin enough to provide a reasonable TAC time. 6.The method of claim 4 wherein said adhesion layer is comprised of analloy of tantalum or an alloy of vanadium.
 7. The method of claim 4wherein said organic electronic device is an OLED, an organictransistor, an organic light sensor, an organic solar cell, or anorganic laser.
 8. The method of claim 4 wherein said encapsulation lidis comprised of glass, or plastic with a barrier layer on said plastic,wherein said barrier layer is nonopaque.
 9. The encapsulated organicelectronic device of claim 1, wherein said encapsulation lid iscomprised of glass.
 10. The encapsulated organic electronic device ofclaim 1, wherein the adhesion layer is directly on the UV-curableadhesive.
 11. The encapsulated organic electronic device of claim 1,wherein the adhesion layer substantially covers one surface of theencapsulation lid.